1. Field of the Invention
This invention relates generally geologic surveys and more particularly to an apparatus and method for acquiring and processing seismic data.
2. Description of the Related Art
Seismic exploration is used to determine the presence of subsurface structures in earth formations that may contain useful materials such as hydrocarbons. A conventional system for conducting seismic survey operations includes acoustic sources, transducers, seismic cables, and a data collection facility. The acoustic source is used to insonify a subterranean formation. The acoustic energy transmitted by the acoustic source radiates generally downwardly into the earth and is partially reflected back towards the earth's surface by subsurface acoustic impedance boundaries, called reflectors, which may exist within the earth. The transducers, which are positioned at or near the earth's surface, are used to detect this reflected acoustic energy. The transducers generate electrical signals proportional to the magnitude of the acoustic energy detected. The seismic cables, which are in communication with the transducers, transmit the electrical signals to the data collection facility for processing.
A conventional survey usually requires the deployment of thousands of transducers and, thus, significant lengths of seismic cables. These seismic cables are formed of cable segments that are joined by connectors. The connectors enable the transmission of data between successive cable segments and, thus, play an integral role in transmitting signals from the transducers to the data collection facility. The connectors can also be adapted to distribute power to the transducers and transmit instructions from the data collection facility to the transducers. Moreover, connectors provided with processors can be configured to convert the analog signals from a transducer into a digital signal. Exemplary seismic survey equipment and arrangements are discussed in U.S. Pat. No. 5,627,798, which is hereby incorporated by reference for all purposes.
Conventional connectors typically have a housing that includes two external electrical plugs that couple to seismic cables. The housing can include a seal that protects the contents of the housing, such as electrical circuitry, from exposure to the environment and means to transfer tension loading from the cable to the housing without subjecting the electrical connectors to this tension.
One conventional connector is disclosed in POT Application No. WO 00/39610, titled “Improved System of Acquiring Geophysical Data” published Jun. 6, 2000 (hereafter the “'610 PCT App.”). The '610 PCT App. describes a box including two cables each having end pieces, first and second electrical plugs, first and second platens, and a cover. Each end piece has a flattened portion. The end pieces are aligned in an opposing fashion such that the flattened portions present a co-planar surface on which the cover mounts. The first platen is disposed within the cover and superposed on the flattened portions. The second platen is fixed on the first platen and supports signal processing equipment. Electrical communication is established between the signal processing equipment and first and second cables via first and second electrical plugs, respectively. Additionally, an O-ring is provided between the cover and connector to seal the box.
It will be appreciated that this conventional connector exemplifies a number of drawbacks. First, this connector requires two electrical plugs. The use of two plugs can necessitate additional fabrication time and increases the number of points of potential failure in the connector. Second, the signal processing equipment is not provided a sealed environment until the cover is secured on the cable ends, i.e., the connector is fully assembled. Thus, field repair or disassembly/assembly of this conventional connector requires unsealing the box and leaving the signal processing equipment exposed to the damaging effects of the elements. Third, the electronics package/processing circuitry cannot be removed from this conventional connector without disassembling the cable string. Thus, the task of changing out only the electronics package inconveniently requires disassembly of the entire box and disconnecting the seismic cables. Fourth, because the electronics package cannot be removed, the electronics package cannot be redeployed in a different location while, for example, the cable is serviced. Thus, this conventional connector increases the number of electronics packages that must be carried in inventory to efficiently carry out survey operations.
Still another drawback is that conventional connectors do not permit the mechanized deployment and retrieval of extended lengths of the cables. Mechanized deployment and retrieval systems typically have opposing tires that draw cable from a drum and spool up cable onto a drum or into a storage container. The opposing tires frictionally engage the cables such that rotation of the tires moves the cables in a desired direction. Unfortunately, some conventional connectors are not configured to pass through these opposing tires because the arrangement of cable and the take-out terminals on conventional connectors are not compact. Rather, such conventional connectors are bulky and include protrusions having angles, which may jam into the tires. Moreover, some conventional connectors have a body length that prevents these connectors from lying flat on the arcuate surface of a drum.
The present invention addresses these and other limitations of conventional connectors.